The scenario involves AOS-CX switches in a two-tier topology (access and core layers) using OSPF routing at the core. The goal is to prevent ARP poisoning attacks on user VLANs at the access layer switches, where end-user devices connect. ARP poisoning (also known as ARP spoofing) is an attack where a malicious device sends fake ARP messages to associate its MAC address with the IP address of another device (e.g., the default gateway), allowing the attacker to intercept traffic.
ARP Inspection (Dynamic ARP Inspection, DAI): This feature prevents ARP poisoning by validating ARP packets against a trusted database of IP-to-MAC bindings. On AOS-CX switches, ARP inspection uses the DHCP snooping binding table to verify that ARP messages come from legitimate devices. If an ARP packet does not match the binding table, it is dropped.
DHCPv4 Snooping: This feature protects against rogue DHCP servers and builds a binding table of legitimate IP-to-MAC mappings by snooping DHCP traffic. The binding table is used by ARP inspection to validate ARP packets. DHCP snooping must be enabled before ARP inspection can function effectively, as it provides the trusted data for validation.
Option A, "ARP inspection," is correct. ARP inspection (DAI) directly prevents ARP poisoning by ensuring that ARP packets are legitimate, making it a key technology for this purpose.
Option B, "OSPF passive interface," is incorrect. OSPF passive interface is used to prevent OSPF from sending routing updates on specific interfaces, typically to reduce routing protocol traffic on user-facing interfaces. It does not prevent ARP poisoning, which is a Layer 2 attack.
Option C, "BPDU guard (protection)," is incorrect. BPDU guard protects against spanning tree protocol (STP) attacks by disabling a port if it receives BPDUs (e.g., from an unauthorized switch). It does not address ARP poisoning, which is unrelated to STP.
Option D, "DHCPv4 snooping," is correct. DHCP snooping is a prerequisite for ARP inspection, as it builds the binding table used to validate ARP packets. It also protects against rogue DHCP servers, which can indirectly contribute to ARP poisoning by assigning incorrect IP addresses.
Option E, "BPDU filtering," is incorrect. BPDU filtering prevents a port from sending or receiving BPDUs, which can be used to protect against STP attacks, but it does not prevent ARP poisoning.
The HPE Aruba Networking AOS-CX 10.12 Security Guide states:
"To prevent ARP poisoning attacks on user VLANs, enable Dynamic ARP Inspection (DAI) on access layer switches. DAI validates ARP packets against the DHCP snooping binding table to ensure they come from legitimate devices. Use the command ip arp inspection vlan to enable DAI on the specified VLANs. DHCP snooping must be enabled first with dhcp-snooping and dhcp-snooping vlan to build the binding table used by DAI." (Page 145, ARP Inspection and DHCP Snooping Section)
Additionally, the guide notes:
"DHCP snooping and ARP inspection work together to protect against Layer 2 attacks like ARP poisoning. DHCP snooping builds a trusted database of IP-to-MAC bindings, which ARP inspection uses to filter out malicious ARP packets." (Page 146, Best Practices Section)
[References:, HPE Aruba Networking AOS-CX 10.12 Security Guide, ARP Inspection and DHCP Snooping Section, Page 145., HPE Aruba Networking AOS-CX 10.12 Security Guide, Best Practices Section, Page 146.===========, , ]
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